Since the discovery of ferrocene in 1951, a number of metallocenes have been prepared by the combination of compounds having the cyclopentadienyl structure with various transition metals. The term "cyclopentadienyl structure" as used herein refers to the following structure. ##STR1##
The term "cyclopentadiene-type compounds" as used herein refers to compounds containing the cyclopentadiene structure. Examples include unsubstituted cyclopentadiene, unsubstituted indene, unsubstituted fluorene, and substituted varieties of such compounds. Also included is tetrahydro indene.
Many of the cyclopentadiene-type metallocenes have been found useful in catalyst systems for the polymerization of olefins. It has been noted in the art that variations in the chemical structure of such cyclopentadienyl-type metallocenes can have significant effects upon the suitability of the metallocene as a polymerization catalyst. For example, the size and location of substitutions on cyclopentadienyl-type ligands has been found to affect the activity of the catalyst, the stereoselectivity of the catalyst, the stability of the catalyst, or other properties of the resulting polymer; however, the effects of various substituents is still largely an empirical matter, that is, experiments must be conducted in order determine just what effect a particular variation will have upon a particular type of cyclopentadienyl-type metallocene.
While there are references in the prior art which have envisioned various unbridged metallocenes, it is considered unlikely that all of the metallocenes within the broad disclosures of publications have actually been prepared and evaluated for their polymerization effects. For example, while U.S. Pat. No. 5,049,534 contains allegations regarding a wide range of both bridged and unbridged metallocenes, the only actual examples of unbridged metallocenes are those in which two identical cyclopentadienyl-type ligands are present.
An object of the present invention is to provide certain new indenyl-containing metallocenes. Still another object of the present invention is to provide polymerization catalysts employing the specific indenyl-type metallocenes. Still yet another object of the present invention is to provide processes for the polymerization of olefins using specific indenyl-type metallocene catalyst systems. Still yet another object of the present invention is to provide polymers produced using such indenyl-containing metallocene catalysts.